The present invention relates generally to the art of producing an 8-level Vestigial Side Band modulated radio frequency signal, and it relates more particularly to a new and improved method and apparatus for generating an HDTV test signal using a single ISA bus computer board for use in demonstrating HDTV products without the need for over-the-air HDTV broadcast signals.
At the present time, broadcast television operates under a standard defined by the National Television Standards Committee. Over the next few years this standard will be phased out and replaced by a new digital television standard defined by the Advance Television Standards Committee for High Definition Television. High Definition Television, HDTV, is synonymous with the standard of the Advance Television Standards Committee, ATSC.
HDTV digital video data is compressed and encoded using the MPEG-II format into a data stream known as the DTV transport layer. The ATSC standard for transmission uses an RF modulation format called 8-VSB, 8 level Vestigial Side Band, as the means to convey the DTV transport layer from a television transmitter to one or more television receivers. Use of the 8-VSB format makes it possible to fit the 19.39 Megabit/second data rate of the DTV transport layer into an RF channel with a bandwidth of only 6 MHz.
Devices used at the present time to generate an 8-VSB modulated RF signal are usually intended for use in a television broadcast application, and are relatively expensive and contained in large enclosures often intended for mounting in a 19 inch equipment rack. Usually, two separate pieces of equipment are required, one being an 8-VSB modulator for converting the HDTV data stream to an 8-VSB intermediate frequency signal, and the other, called an RF modulator, for converting the IF signal to an RF signal. A typical RF modulator is capable of generating an RF signal on any of several broadcast or cable television channels.
During the transition period between the current NTSC television broadcast standard and the new ATSC television broadcast standard very few live HDTV signals are being transmitted, wherefore a need exists in the industry for a compact, inexpensive device to allow manufacturers and retailers of HDTV products to demonstrate HDTV to the general public.
Briefly, there is provided in accordance with the present invention a new and improved method and apparatus a device which combines the functions of an 8-VSB modulator and an RF modulator and is totally contained on a single ISA computer board that plugs into an ISA computer slot eliminating the need for a separate enclosure and dedicated power supply for each modulator, thereby reducing the space required and the cost thereof. Moreover, since only one channel is required for demonstrating HDTV, this invention further reduces the cost of the necessary circuitry to generate all broadcast and cable television channels.